Look at the dates on the uses of these exotic temperature controllers.
Organic compounds and positive temp coefficients and so on. All these were
used before the current era. Today all you need is a reliable way to
measure the error between the crystals' current temperature and the set
point.
Those exotic methods were good back when controllers were analog devices
build with op-amps and precision resisters and every math operation cost
you one more op-amp. Today we can do a million floating point operations
per second for the cost of one kind good op-amp.
The trick with using a uP and it's built-in A/D converters is scale. You
want the limited 10-bits of revolution to fall over the operating range
which is very narrow, like 1C. Anything outside of that is either 0000 or
1111 and only seen at start-up., So at start up the the controller is on
"bang-bang" mode then later you have milli-degree resolution over your 1C
range. Basically you are measuring noise. but your $2 uP can take 100,000
measurments per second and putt tour a digital filter.
Today we can do things the old-time designers even as recent as the 1980's
would not even dream of doing and it cost under $10.
On Mon, Jun 5, 2017 at 1:35 AM, Ulf Kylenfall via time-nuts <
time-nuts at febo.com> wrote:
> The Crystal heater clip wasa Murata "Posistor" soldered onto a clipand
> they were marketed by Murata.
> I once purchased a small amount of theseand used them as "poor man's
> ovens".
> Although not perfect by far, they did theirjob and kept my UHF gear stable.
> Murata dropped that product many yearsago and I have not been able to
> findany similar product. The Posistors arelisted by eg. Digi-key but they
> do not stock them.
> Ulf - SM6GXV
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--
Chris Albertson
Redondo Beach, California